javax validation size trim whitespace

At first Spring will use setter-method to set value of property. And for validate value Spring will get it with getter-method. That means, you can trim value in setter-method for prepare it to validation:

public class User {
    @NotBlank
    @Size(min = 2)
    private String name;

    public void setName(String value){
        this.name = value.trim();
    }

    public String getName(){
        return this.name;
    }
}